This invention relates in general to electrostatographic imaging members and more specifically, to seamed electrostatographic imaging members having a permanent localized solid attribute to enable avoidance of imaging on the seam and processes and apparatus for using these imaging members.
Flexible electrostatographic belt imaging members are well known in the art. Typical electrostatographic flexible belt imaging members include, for example, photoreceptors for electrophotographic imaging systems and electroceptors such as ionographic imaging members for electrographic imaging systems. Generally, these belts comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymeric matrix material. The "imaging layer" as employed herein is defined as the dielectric imaging layer of an electroceptor belt and the photoconductive imaging layer of an electrophotographic belt. The photoconductive imaging layer may comprise a single photoconductive layer or a plurality of layers such as a combination of a charge generating layer and a charge transport layer.
Flexible electrophotographic imaging member belts are usually multilayered photoreceptors that comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer. A typical layered photoreceptor having separate charge generating (photogenerating) and charge transport layers is described in U.S. Pat. No. 4,265,990, the entire disclosure thereof being incorporated herein by reference. The charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
The flexible electrostatographic imaging member belt is fabricated from a sheet cut from a web containing thermoplastic polymeric material. The sheets are usually rectangular in shape. All edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheets are formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable technique. Typical joining techniques include welding (e.g., ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic welding is generally the preferred method of joining because it is rapid, clean (no solvents or other fumes) and produces a thin and narrow seam. In addition, ultrasonic welding is favored because it causes generation of heat, only at the contiguous overlapping end marginal regions of the sheet, to maximize melting of one or more layers therein.
In a typical electrophotographic imaging process, a photoreceptor surface is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoreceptor surface is exposed to a light pattern. Exposure of the charged photoreceptor surface selectively dissipates the charges thereon in the irradiated areas. This process forms an electrostatic latent image on the photoreceptor surface. After the electrostatic latent image is formed on the photoreceptor surface, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles. The toner particles are attracted to the latent image to form a toner image on the photoreceptor surface. The toner image is then transferred from the photoreceptor surface to a receiving sheet. The toner particles are heated to permanently affix the image to the receiving sheet. After each transfer process, any toner residue remaining on the photoreceptor surface may be cleaned by a suitable cleaning device.
In a system of the foregoing type, a seamed flexible multilayered photoreceptor belt is often used. The seam of the belt is not a desirable location for forming images thereon due to the presence of surface discontinuities along the seam which cause the seam itself to be printed out on the receiving sheet. To prevent printing on the seam of seamed photoreceptor belts, a timing hole is punched through the ground strip which runs along one edge of the belt. The hole is located in the ground strip at a predetermined distance from the seam and from nearest outer edge of the belt. This hole is detected by a dedicated detector as the hole passes a predetermined position along the imaging path of the photoreceptor so that the seam can be tracked to prevent formation of electrostatic latent images on the seam. Unfortunately, the hole in the seam allows debris to pass through it to form undesirable deposits on critical machine components. Moreover, the hole punching operation requires sophisticated equipment for aligning the seam and punching the hole in the belt. Further, the dedicated detector comprises a light source on one side of the belt and a light detector on the other side of the belt as well as a power source and appropriate electrical connections, which adds to the imaging machine manufacturing cost. Thus, there is a need for an improved system to locate the position of the seam without using a dedicated detecting sensor in combination with a hole through the ground strip of the belt.
In copying or printing systems, such as a xerographic copier, laser printer, or ink-jet printer, a common technique for monitoring the quality of prints is to artificially create a "test patch" of a predetermined desired density. The actual density of the printing material (toner or ink) in the test patch can then be optically measured to determine the effectiveness of the printing process in placing this printing material on the print sheet.
In the case of xerographic devices, such as a laser printer, the surface that is typically of most interest in determining the density of printing material thereon is the charge-retentive surface or photoreceptor, on which the electrostatic latent image is formed and subsequently, developed by causing toner particles to adhere to areas thereof that are charged in a particular way. In such a case, the optical device for determining the density of toner on the test patch, which is often referred to as a toner area coverage sensor or "densitometer", is disposed along the path of the photoreceptor, directly downstream of the development of the development unit. There is typically a routine within the operating system of the printer to periodically create test patches of a desired density at predetermined locations on the photoreceptor by deliberately causing the exposure system thereof to charge or discharge as necessary the surface at the location to a predetermined extent.
The test patch is then moved past the developer unit and the toner particles within the developer unit are caused to adhere to the test patch electrostatically. The denser the toner on the test patch, the darker the test patch will appear in optical testing. The developed test patch is moved past a densitometer disposed along the path of the photoreceptor, and the light absorption of the test patch is tested; the more light that is absorbed by the test patch, the denser the toner on the test patch. Xerographic test patches are traditionally printed in the interdocument zones on the photoreceptor. Generally each patch is about an inch square that is printed as a uniform solid half tone or background area. Thus, the traditional method of process controls involves scheduling solid area, uniform halftones or background in a test patch. Some of the high quality printers contain many test patches.